1. Field of the Invention
The present invention relates to a vapor-deposited film performing a gas barrier function and used for packaging technique, for example, foodstuff, medicines, or precision electronic parts.
2. Description of the Related Art
A packaging material for packaging foodstuff, medicines, precision electronic parts, etc. is required to perform a sufficient gas barrier function.
In order to suppress the change of properties of the packaged material, a packaging material performing a gas barrier function is capable of preventing oxygen, water vapor, etc. permeating through the packaging material so as to prevent the effects of the gaseous material deteriorating the packaged contents. Where, for example, foodstuff is packaged by the packaging material performing the gas barrier function, the capability of shutting off oxygen, water vapor, etc. noted above is intended to suppress the oxidation and change of properties of proteins as well as fats and oils and to maintain the taste and the freshness of the packaged foodstuff. Where medicines are packaged by the particular packaging material, the capability is intended to maintain the sterility, to suppress the change of properties of the effective components and to maintain the performance. Further, where precision electronic parts are packaged by the particular packaging material, the capability is intended to prevent the corrosion of the metal portion and to prevent defective insulation.
Known packaging materials performing a gas barrier function include, for example, a packaging film using a polymer resin composition said to have a relatively high gas barrier function, such as a polypropylene film (KOP) coated with vinylidene chloride resin, a polyethylene terephthalate (KPET) film coated with vinylidene chloride resin and an ethylene-vinyl alcohol copolymer (EVOH) film; a foil of a metal such as aluminum or a foil of a metal compound; and a metal vapor-deposited film prepared by vapor deposition of a metal such as aluminum or a metal compound on a suitable polymer resin composition, even if the resin composition itself, when used singly, does not perform a high gas barrier function.
The packaging film using the polymer resin composition noted above is inferior in its gas barrier function to the foil using a metal such as aluminum or a metal compound, and to the metal vapor-deposited film prepared by forming a vapor-deposited film of a metal or a metal compound. Also, the packaging material using the polymer resin composition is likely to be affected by temperature and humidity, and the gas barrier function of the particular packaging material is likely to be further deteriorated by a change in temperature or humidity.
On the other hand, the foil made of a metal such as aluminum or a metal compound and the metal vapor-deposited film prepared by forming a vapor deposition layer are less likely to be affected by the temperature and the humidity so as to produce an excellent gas barrier function. However, the foil and the metal vapor-deposited film noted above are defective in that it is impossible to visually confirm the packaged material through the foil or the metal vapor-deposited film.
Under the circumstances, a vapor-deposited film prepared by forming a ceramic thin film made of, for example, a metal oxide and a silicon oxide on a substrate consisting essentially of a polymer material having a transparency has been put on the market as a packaging material satisfying both the gas barrier function and the transparency.
Aluminum oxide attracts a lot of attention as a material of the ceramic thin film because of the low cost of the raw material and the transparency.
However, a film prepared by forming an aluminum oxide film by the vapor deposition is low in the adhesion of the vapor-deposited film to the substrate so as to give rise to the defect that, if a treatment such as a retort treatment is applied, delamination is brought about.
Also, it has been attempted to date to improve the adhesion of the metal oxide vapor deposition layer on a plastic substrate by applying an in-line pretreatment using a plasma. However, in the case of using the conventional plasma generating apparatus, it is impossible to obtain a high treating effect, leading to a high cost.
Among the plasma generating apparatus, an apparatus of a DC discharge system certainly permits generating plasma easily. However, if it is intended to obtain a high bias voltage, the plasma mode is changed from the glow into the arc, giving rise to the problem that a strong treatment cannot be applied to a large area.
Also, a plasma generating apparatus of a high frequency discharge system, which certainly permits generating a stable plasma over a large area, is defective in that a high self bias voltage cannot be expected.
The present invention, which has been achieved in view of the situation described above, provides a vapor-deposited film prepared by forming by vapor deposition a ceramic thin film made of, for example, a metal oxide or a silicon oxide on a substrate consisting essentially of a polymer material having a transparency and is intended to strengthen the adhesion of the vapor-deposited film to the substrate so as to prevent the delamination caused by the treatment such as the retort treatment.